Allah concludes surah al-Fath by saying:
مُّحَمَّدٌ رَّسُولُ اللَّهِ ۚ وَالَّذِينَ مَعَهُ أَشِدَّاءُ عَلَى الْكُفَّارِ رُحَمَاءُ بَيْنَهُمْ ۖ تَرَاهُمْ رُكَّعًا سُجَّدًا يَبْتَغُونَ فَضْلًا مِّنَ اللَّهِ وَرِضْوَانًا ۖ سِيمَاهُمْ فِي وُجُوهِهِم مِّنْ أَثَرِ السُّجُودِ ۚ ذَٰلِكَ مَثَلُهُمْ فِي التَّوْرَاةِ ۚ وَمَثَلُهُمْ فِي الْإِنجِيلِ كَزَرْعٍ أَخْرَجَ شَطْأَهُ فَآزَرَهُ فَاسْتَغْلَظَ فَاسْتَوَىٰ عَلَىٰ سُوقِهِ يُعْجِبُ الزُّرَّاعَ لِيَغِيظَ بِهِمُ الْكُفَّارَ ۗ وَعَدَ اللَّهُ الَّذِينَ آمَنُوا وَعَمِلُوا الصَّالِحَاتِ مِنْهُم مَّغْفِرَةً وَأَجْرًا عَظِيمًا
Muhammad is the Messenger of Allah. And those with him are stern toward the disbelievers, merciful among themselves. You see them bowing and prostrating, seeking bounty from Allah and His pleasure. Their sign is on their faces from the traces of prostration. That is their description in the Tawrah. And their description in the Injeel is like a plant which produces its offshoots and strengthens them so that they grow firm and stand up on their stalks, delighting the farmers – so that He may enrage the disbelievers with them. Allah has promised those of them who believe and do righteous deeds forgiveness and a great reward. [48:29]
In the midst of this ayah, Allah struck the parable:
وَمَثَلُهُمْ فِي الْإِنجِيلِ كَزَرْعٍ أَخْرَجَ شَطْأَهُ فَآزَرَهُ فَاسْتَغْلَظَ فَاسْتَوَىٰ عَلَىٰ سُوقِهِ يُعْجِبُ الزُّرَّاعَ لِيَغِيظَ بِهِمُ الْكُفَّارَ
And their description in the Injeel is like a plant which produces its offshoots and strengthens them so that they grow firm and stand up on their stalks, delighting the farmers – so that He may enrage the disbelievers with them.
In his book of tafsir, Imam al-Baghawi briefly summarized the meaning of this parable by writing:
هذا مثل ضربه الله – عز وجل – لأصحاب محمد – صلى الله عليه وسلم – في الإنجيل [ أنهم يكونون قليلا ثم يزدادون ويكثرون . قال قتادة : مثل أصحاب رسول الله – صلى الله عليه وسلم – في الإنجيل ] مكتوب أنه سيخرج قوم ينبتون نبات الزرع يأمرون بالمعروف وينهون عن المنكر . ـ
This is a parable that Allah struck regarding the companions of Muhammad in the Injeel. It describes them as being few in number, then growing and increasing.